/*
 * Copyright 2002-2007 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.force4spring.support;

import java.io.IOException;

import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.force4spring.SessionFactoryUtils;
import org.force4spring.SessionHolder;
import org.springframework.dao.DataAccessResourceFailureException;
import org.springframework.transaction.support.TransactionSynchronizationManager;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;
import org.springframework.web.filter.OncePerRequestFilter;

/**
 * Servlet 2.3 Filter that binds a Force.com Session to the thread for the entire
 * processing of the request. Intended for the "Open Session in View" pattern,
 * i.e. to allow for lazy loading in web views despite the original transactions
 * already being completed.
 *
 * <p>This filter makes Force.com Sessions available via the current thread, which
 * will be autodetected by transaction managers. It is suitable for service layer
 * transactions via {@link org.force4spring.ForceTransactionManager}
 * or {@link org.springframework.transaction.jta.JtaTransactionManager} as well
 * as for non-transactional read-only execution.
 *
 * <p>Looks up the SessionFactory in Spring's root web application context.
 * Supports a "sessionFactoryBeanName" filter init-param in <code>web.xml</code>;
 * the default bean name is "sessionFactory". Looks up the SessionFactory on each
 * request, to avoid initialization order issues (when using ContextLoaderServlet,
 * the root application context will get initialized <i>after</i> this filter).
 *
 * @author Juergen Hoeller
 * @author Max Rudman
 * @since 04.19.2009
 * @see #setSingleSession
 * @see #lookupSessionFactory
 * @see OpenSessionInViewInterceptor
 * @see org.force4spring.ForceInterceptor
 * @see org.force4spring.ForceTransactionManager
 * @see org.force4spring.SessionFactoryUtils#getSession
 * @see org.springframework.transaction.support.TransactionSynchronizationManager
 */
public class OpenSessionInViewFilter extends OncePerRequestFilter {
	public static final String DEFAULT_SESSION_FACTORY_BEAN_NAME = "sessionFactory";

	private String sessionFactoryBeanName = DEFAULT_SESSION_FACTORY_BEAN_NAME;


	/**
	 * Set the bean name of the SessionFactory to fetch from Spring's
	 * root application context. Default is "sessionFactory".
	 * @see #DEFAULT_SESSION_FACTORY_BEAN_NAME
	 */
	public void setSessionFactoryBeanName(String sessionFactoryBeanName) {
		this.sessionFactoryBeanName = sessionFactoryBeanName;
	}

	/**
	 * Return the bean name of the SessionFactory to fetch from Spring's
	 * root application context.
	 */
	protected String getSessionFactoryBeanName() {
		return this.sessionFactoryBeanName;
	}

	protected void doFilterInternal(
			HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
			throws ServletException, IOException {

		SessionFactory sessionFactory = lookupSessionFactory(request);
		boolean participate = false;

		if (TransactionSynchronizationManager.hasResource(sessionFactory)) {
			// Do not modify the Session: just set the participate flag.
			participate = true;
		}
		else {
			logger.debug("Opening single Force Session in OpenSessionInViewFilter");
			ForceSession session = getSession(sessionFactory);
			TransactionSynchronizationManager.bindResource(sessionFactory, new SessionHolder(session));
		}

		try {
			filterChain.doFilter(request, response);
		}

		finally {
			if (!participate) {
				SessionHolder sessionHolder =
						(SessionHolder) TransactionSynchronizationManager.unbindResource(sessionFactory);
				logger.debug("Closing single Hibernate Session in OpenSessionInViewFilter");
				closeSession(sessionHolder.getSession(), sessionFactory);
			}
		}
	}

	/**
	 * Look up the SessionFactory that this filter should use,
	 * taking the current HTTP request as argument.
	 * <p>Default implementation delegates to the <code>lookupSessionFactory</code>
	 * without arguments.
	 * @return the SessionFactory to use
	 * @see #lookupSessionFactory()
	 */
	protected SessionFactory lookupSessionFactory(HttpServletRequest request) {
		return lookupSessionFactory();
	}

	/**
	 * Look up the SessionFactory that this filter should use.
	 * <p>Default implementation looks for a bean with the specified name
	 * in Spring's root application context.
	 * @return the SessionFactory to use
	 * @see #getSessionFactoryBeanName
	 */
	protected SessionFactory lookupSessionFactory() {
		if (logger.isDebugEnabled()) {
			logger.debug("Using SessionFactory '" + getSessionFactoryBeanName() + "' for OpenSessionInViewFilter");
		}
		WebApplicationContext wac = WebApplicationContextUtils.getRequiredWebApplicationContext(getServletContext());
		return (SessionFactory) wac.getBean(getSessionFactoryBeanName(), SessionFactory.class);
	}

	/**
	 * Get a ForceSession for the SessionFactory that this filter uses.
	 * Note that this just applies in single session mode!
	 * <p>The default implementation delegates to SessionFactoryUtils'
	 * getSession method.
	 * <p>Can be overridden in subclasses for creating a Session with a custom
	 * entity interceptor or JDBC exception translator.
	 * @param sessionFactory the SessionFactory that this filter uses
	 * @return the Session to use
	 * @throws DataAccessResourceFailureException if the Session could not be created
	 * @see org.force4spring.SessionFactoryUtils#getSession(SessionFactory, boolean)
	 */
	protected ForceSession getSession(SessionFactory sessionFactory) throws DataAccessResourceFailureException {
		return openSession(sessionFactory);
	}

	/**
	 * Get a Session for the SessionFactory that this filter uses.
	 * Note that this just applies in single session mode!
	 * <p>The default implementation delegates to the
	 * <code>SessionFactoryUtils.getSession</code> method.
	 * <p>Can be overridden in subclasses for creating a Session with a
	 * custom entity interceptor or JDBC exception translator.
	 * @param sessionFactory the SessionFactory that this filter uses
	 * @return the Session to use
	 * @throws DataAccessResourceFailureException if the Session could not be created
	 * @see org.force4spring.SessionFactoryUtils#getSession(SessionFactory, boolean)
	 */
	protected ForceSession openSession(SessionFactory sessionFactory) throws DataAccessResourceFailureException {
		ForceSession session = SessionFactoryUtils.getSession(sessionFactory, true);
		return session;
	}

	/**
	 * Close the given Session.
	 * Note that this just applies in single session mode!
	 * <p>Can be overridden in subclasses, e.g. for flushing the Session before
	 * closing it. See class-level javadoc for a discussion of flush handling.
	 * Note that you should also override getSession accordingly, to set
	 * the flush mode to something else than NEVER.
	 * @param session the Session used for filtering
	 * @param sessionFactory the SessionFactory that this filter uses
	 */
	protected void closeSession(ForceSession session, SessionFactory sessionFactory) {
		SessionFactoryUtils.closeSession(session);
	}

}
